1. Field of the Invention
The present invention relates to an image quality improving apparatus and method, and more particularly, an image quality improving apparatus and method that can distinguish an edge of an actual outline imagery recognized in an image inputted via an image input unit from those printed according to dither patterns to emphasize the actual outline, and thereby acquire the image without distortion.
2. Description of the Related Art
An image quality improving apparatus serves to convert an image into a form that can be easily seen by the human. An example of such an image improving apparatus and method is disclosed from Korean Patent Application Publication No. 10-2002-59531, entitled “Apparatus and Method of Improving Printing Quality in Documents Containing a Mixture of Text and Image.”
The apparatus and method disclosed by the above document will be described in brief as follows.
First, the apparatus according to the above document may generally include a detecting section and an emphasizing section.
From pixels in an output picture containing a mixture of a text and an image, the detecting section detects pixels corresponding to an outline and to the text.
The emphasizing section adjusts the lightness of the pixels detected by the detecting section to emphasize the output of the detected pixels. Herein, values multiplied with weights are added to the lightness values of those pixels surrounding a target pixel, and it is judged whether the resultant values exceed a predetermined reference value, to judge whether the target pixel corresponds to the outline based upon the result of judgment.
Also, to determine whether a specific pixel is a text, those pixels surrounding the specific pixel are grouped according to their lightness differences, and it is judged whether the number of groups is smaller than a reference number.
As a consequence, only those pixels corresponding to the outline of the text are emphasized to execute differentiated emphasis conforming to characteristics of the text and the image to thereby improve the quality of the output document.
But this solution has a limited capability in reflecting characteristics around the specific or target pixel, since it only uses a single window in calculation of a connected component number N of the pixels. As a result, in a document printed via a low Line Per Inch (LPI) condition, such as a newspaper in which characteristics around a target pixel are similar to a letter, there are problems in that edge detection precision is poor, or a large quantity of memory and complex calculation are required.
According to a conventional technique, binary data are extracted through comparison with a mean value of a single window mask to calculate connected components in order to sort edge pixels based upon the connected components. But if a printed object wanted by a user is obtained in a dither pattern, the printed object is printed differently, according to the application of frequency characteristics with respect to the dither pattern. Accordingly, if a single mask is used, there is a problem in that this technique can rarely correspond to various frequency patterns.
For example, in case of a halftone having a low frequency, a text is hardly distinguishable from an image at a small window size. Even if the printed object is obtained at a large window size in a halftone pattern of an equal frequency, an edge is not easily distinguished since the degree of variation is different according to pixel position.
In a case of extracting binary data through comparison with the mask mean value, the number of those, which are judged 1, from total 9 pixels is different according to masks. Even if the patterns are the same, the variation of value results in different values of connected components, and thus it is difficult to realize a desired object.
Further, since binary data are processed based upon a mean value within a window mask, the number of pixels having a binary data value of 1 is not constant. Therefore, if an edge is formed diagonally, the probability of erroneous sorting between a text edge and a halftone image edge disadvantageously increases.